Before being plagued by the Sphinx,
Thebes was plagued by a fox.
It was the swiftest little animal there was.
It ran like a streak through the city
seizing whatever it wished, utterly unstoppable.
To protect the city,
whose seven musical walls were insufficient apparently,
each year the citizens
were forced to offer as a forfeit to the fox
a human child. 

But the Thebans had an ally in a certain hero from Attica,
who was in possession of a hound,
who in turn possessed this attribute:
that whatever he set upon could not possibly escape.
Unstoppable fox, inescapable hound. Thebes. 

In the end,
as if in expression or abhorrence of the paradox,
Zeus turned both beasts to stone.